The invention relates to a device, or tool, for threading and unthreading a stud, or fastening member, into and out of a vessel, such as a reactor vessel.
The cover of a vessel such as a reactor is generally secured by studs which pass thru holes in the vessel and are pre-tensioned to securely hold the cover in place. Normally, the studs extend above the cover so that either the cover would have to be lifted off the studs, or, as is generally more convenient because of space limitations after the studs are detensioned, the studs are removed from the vessel.
In many cases, the vessel is housed in a structure and the studs project upwardly from the vessel with a cover placed over the vessel opening. When the studs are detensioned, the cover cannot be lifted over the projecting studs because of space limitations.
It is known to drive studs into and out of a pressure vessel using an air motor which forms part of a tool suspended from a crane which lowers or raises the tool. When lowered, a socket at the lower end of the tool fits over a collar on the stud. With the stud lowered into a hole in the vessel, the crane operator controls an air motor which causes the stud to rotate in one or the other direction, depending upon whether the stud is threaded into or out of the vessel.
Since the studs are large and each weigh between 500 and 1000 pounds, they produce a counter-torque which can be dangerous because the controls are such that the operator takes up the torque. Despite the fact that the tool incorporates a reduction gear which reduces the torque absorbed by the operator, if the operator does not exercise due care, and activates the control inadvertently, he could be caught off balance, and be seriously injured.